docs: def spkopa(filename):
      """
      Open an existing SPK file for subsequent write.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/spkopa_c.html
  
      :param filename: The name of an existing SPK file.
      :type filename: str
      :return: A handle attached to the SPK file opened to append.
      :rtype: int
      """
      filename = stypes.stringToCharP(filename)
      handle = ctypes.c_int()
      libspice.spkopa_c(filename, ctypes.byref(handle))
      return handle.value